The present disclosure relates to image forming apparatuses that form an image on a recording medium such as paper. More particularly, the present disclosure relates to a method for estimating the attachment condition of discharge products to the surface of a photosensitive member on which a photosensitive layer and a surface protection layer are formed, and thereby preventing image defects such as image deletion.
In image forming apparatuses such as printers, copiers, facsimile machines, and multifunctional peripherals having their functions integrated together, as a photosensitive drum, which is an example of an image carrying member, an amorphous silicon photosensitive member having formed on its surface an amorphous silicon layer, or an organic photosensitive member having formed on its surface an organic photosensitive layer, is widely used. With a view to improving the stability of image quality over a long period of time and thereby achieving a prolonged life of the photosensitive drum, a photosensitive member that has formed on it a surface protection layer which protects the surface of the photosensitive layer is used. For example, an amorphous silicon photosensitive member has formed on it a surface protection layer comprising amorphous silicon carbide or amorphous carbon which has a higher hardness and which excels in wear resistance and print resistance.
If the above-described surface protection layer is oxidized in the process of the electrostatic charging of the photosensitive layer, or is soiled with active substances such as ozone, NOx, and SOx and their reaction products, that is, so-called discharge products, in a high-humidity environment, the oxidized part or the discharge products adsorb moisture, forming a low-resistance layer. As a result, the electric charge of a latent image may inconveniently flow in the planar direction, causing the image to blur, or to ooze as if rubbed against, that is, so-called image deletion is inconveniently made more likely to occur.
As a solution, various methods have been proposed for removing an oxidized part of the photosensitive layer and discharge products attached to the photosensitive layer and thereby preventing image deletion. For example, according to one known method, the surface condition of the photosensitive member is detected by use of the driving torque of the photosensitive member, and polishing conditions such as the pressing force and the rotation speed of the rubbing member are changed based on the result of detection. According to another known method, the driving torque of the cleaning brush is measured, and the amount of toner left unused on the photosensitive member is controlled based on the result of detection.